The present invention relates to a rubber composition for an inner liner.
Tires having low heat generation and a light weight have been recent design goals based on the social desire for a low fuel cost car and a light weight inner liner provided on the inside of a tire. The inner liner is desired to serve the functions of reducing the quantity of air leaks (air permeation quantity) from the inside of a tire with air to the outside and improving air retention properties.
At present, as a rubber composition for an inner liner, the improvement of the air retention property of a tire is obtained by employing butyl base rubber and diene rubber, mainly constituting a butyl base rubber. Butyl base rubber is superior in lowering air permeation, but the hysteresis loss of the rubber composition obtained is large and there have been problems in that the the higher the amount of butyl base rubber used, the greater the heat generation in the tire and the lower the fuel-economy property of the car.
Also, there has been a problem in that when the ratio of natural rubber is increased for improving the fuel-economy property, the quantity of air permeation is also increased.
The Japanese Unexamined Patent Publication No. 11-140234 discloses a rubber composition for an inner liner comprising platy mica. However, the composition does not adequately improve the air retention property of a tire and does not reduce rolling resistance and further, there was a problem in that cracks are generated in the inner liner.